Voltage regulator device

ABSTRACT

A voltage regulator device ( 10 ) is described, applicable to the electrical system of a motor vehicle of the type comprising at least an electrical machine consisting of a three-phase generator and at least an accumulator ( 12 ). The voltage regulator device ( 10 ) comprises a rectifier bridge and a voltage rising circuit ( 16 ) provided with a first series of power elements ( 20 ). The voltage rising circuit ( 16 ) comprises one or more inductors ( 14 ) the winding inductance of stator phase of which is exploited in order to raise the phase voltage above the level of the voltage provided by the accumulator ( 12 ), so that it is possible to supply current to the electrical loads of the vehicle since a very low rotation regime of the engine of the vehicle itself.

The present invention relates to a voltage regulator device, inparticular applicable to the electrical system of a motor vehicle, suchas a motor cycle.

A voltage regulator or stabilizer is a device intended to be interposedbetween an electrical power generator and one or more electrical loads.The voltage regulator or stabilizer receives an input voltage having avariable value in a preset time period, and produces an output voltagehaving a preset, accurate, and stable value, independently from thecurrent intensity absorbed by the electrical load.

The electrical and electronic components of the motor vehicles ingeneral, with particular reference to the motor cycles, are usuallycapable of absorbing a maximum voltage that is not particularly high,and can also be severely damaged by a voltage oscillation. Vice versa, avoltage lowering can involve a power supply that is insufficient for theproper functioning of the vehicle. Therefore, the use of voltageregulators on the motor vehicle allows maintaining a voltage within therange that the electrical or electronic component of the vehicle itselfcan accept without incurring in malfunctionings.

The state of the art for the shunt voltage regulators for automotiveapplications provides for the use of a diode bridge in order to convertthe signals provided by the three-phase voltage generator, dragged bythe endothermic engine of the vehicle, into a continuous voltage, to beable to recharge the accumulator (battery) that is present on thevehicle itself. Such a voltage regulator is represented by the principlescheme shown in the following FIG. 1.

In FIG. 2, the variation in time of the three sinusoidal waves producedby the vehicle voltage generator is schematized. These sinusoidal wavesturn out to be mutually offset by 120°. These sinusoidal signals aremade completely positive by the use of the three-phase diode bridge,thus obtaining for each phase the signal trend as illustrated in FIG. 3.Since the diode bridge acts as an envelop detector, the obtained exitingwaveform is the one represented in FIG. 4.

The management of the regulation takes place by means of three furtherpower elements, such as, for example, thyristors or SCR (“SiliconControlled Rectifiers”), which are activated upon reaching the maximumvoltage of the battery and which provide to short-circuit to ground,throughout the entire duration of a half wave, the voltage generator. Inthis manner, no further energy is supplied to the battery, an thevoltage of the battery itself does not rise further.

The main drawback of the voltage generators of the known type is due toa low efficiency, relating to all three operative phases of the voltagegenerator, that is:

1) during the power supply phase towards the battery, where there is ayield ranging between 70% and 80% due the voltage loss that takes placeon the diodes of the bridge, that are run through by the entire currentprovided by the generator;

2) during the regulation phase, where a mechanical power loss takesplace, since the entire current provided by the generator run throughthe control thyristors. The mechanical power loss is internallydissipated in the form of heat;

3) during the ignition phase, where the generator voltage does notexceed the battery voltage level and it is not possible to supply energytowards the battery itself, since the diodes of the rectifier bridge arein a condition of inverse biasing, therefore they are prevented fromconducting.

The consequence of the first two aspects is that the electrical energygeneration system installed on the motor vehicles has to be oversizedcompared to the real needs, so as to account for the losses in thevoltage regulation system, with a consequent increase in the fuelconsumptions and pollutant emissions. In addition, the voltage regulatordevices of the known type need a suitable heat dissipation apparatus,such as, for example, the one shown in FIG. 5.

Instead, this latter aspect limits the possibility to produce engineswith a low minimum regime, as well as the possibility to startelectronic injection-supplied vehicles, in the absence of a battery, bymeans of the use of kick-starters. This latter problem relates inparticular to motor cycles and mopeds.

Therefore, the object of the present invention is to produce a voltageregulator device, applicable in particular to the electrical system of amotor vehicle, which is capable of solving the above-mentioned drawbacksof the prior art in an extremely simple, economic, and particularlyfunctional manner.

In detail, it is an object of the present invention to produce a voltageregulator device that is capable of transferring almost entirely theenergy available from the electrical machine (generator) towards thebattery.

Another object of the invention is to produce a voltage regulator devicethat avoids dissipating energy on the diodes of the rectifier bridge,thus reducing the voltage loss on the power elements.

Another object of the invention is to produce a voltage regulator devicethat does not need particularly complex and bulky heat dissipationsystems.

These objects according to the present invention are achieved byproducing a voltage regulator device, applicable in particular to theelectrical system of a motor vehicle, as set forth in claim 1.

Further characteristics and advantages of a voltage regulator deviceaccording to the present invention are highlighted by the followingdescription, given by way of non-limiting example, with reference to theannexed schematic drawings, in which:

FIG. 1 shows the principle scheme of a voltage regulator device producedaccording to the prior art;

FIG. 2 is a graph illustrating the variation in time of the threesinusoidal signals produced by the voltage generator of a general motorvehicle;

FIG. 3 is a graph illustrating the signals of FIG. 2 after they havebeen rectified by a three-phase diode bridge;

FIG. 4. is a graph illustrating the waveform of the output voltage fromthe voltage regulator device of FIG. 1;

FIG. 5 illustrates a heat dissipation element, applicable to a voltageregulator device as that shown in FIG. 1;

FIG. 6 illustrates a step-up circuit, o voltage rising circuit,applicable to a voltage regulator device according to the presentinvention;

FIG. 7 illustrates the entire circuit of the voltage regulator deviceaccording to the present invention; and

FIG. 8 is a block scheme illustrating the functioning of the voltageregulator device according to the present invention.

With particular reference to FIGS. 6 to 8, a voltage regulator deviceaccording to the present invention is shown, applicable in particular tothe electrical system of a motor vehicle, in particular a motor cycle,and generally indicated with the reference number 10. In detail, theelectrical system of the motor vehicle is of the type comprising atleast one electrical machine (not shown), typically a three-phasegenerator (alternator), and at least one accumulator 1, such as, forexample, a common 12 Volt battery.

In order to optimize the battery recharge system 12 to a minimumrotation regime of the vehicle, it is necessary to transfer almostentirely the energy available from the electrical machine towards thebattery 12 itself. This is obtained by exploiting, in the voltageregulator device 10 according to the invention, the winding inductanceof stator phase of one or more inductors 14 to implement a step-upcircuit 16, or voltage riser, which allows rising the phase voltageabove the level of the voltage provided by the battery 12, so that it ispossible to supply current to the electrical loads of the vehicle sincea very low rotation regime of the engine, according to the principlescheme shown in FIG. 6.

Substantially, during the closure of the switch on the lower part of therectifier bridge, energy is stored in the inductors 14. This energy isreturned to the opening of the switch as an extra voltage, allowingtriggering the three diodes 18 that are present in the upper part of therectifier bridge, therefore allowing supplying energy towards thebattery 12.

The step-up circuit 16 has to be produced with power elements 20,controllable at any time, both in closing and opening, on the lower partof the rectifier bridge, as well as the above-mentioned diodes 18arranged in the upper part of the rectifier bridge. According to theinvention, such power elements 20 consist of a first series of three Nchannel field-effect transistors of the MOSFET type, wherein it ispossible to use the respective wheeling diodes 22 as rectifier elementsand the channel closure in order to perform the regulating and raisingvoltage functions (step-up) according to the principle scheme shown inFIG. 6.

In order to optimize the yield of the voltage regulator device 10 duringthe functioning, a measure has been introduced to avoid dissipatingenergy on the diodes 18 of the rectifier bridge, by reducing the voltageloss on the power elements.

This measure provides that also in the upper part of the rectifierbridge a second series of power elements 24 is provided for, thatconsist of three N channel field-effect transistors of the MOSFET type,according to the principle scheme shown in FIG. 7. Among suchfield-effect transistors of the MOSFET type 24, it is possible to usethe wheeling diodes 26 as rectifier elements during the step-up phase.Instead, the wheeling diodes 26 are by-passed at the end of the step-upphase.

Substantially, when exceeding the rotation regime value of the enginebeyond which the step-up measure does not contribute anymore, the firstMOSFET series 20 and the second MOSFET series 24 of the rectifier bridgeare driven in a synchronous manner with the three half waves generatedby the three-phase generator.

Each MOSFET 20, 24 is driven with a separate drive in the instant whenthe relative wheeling diode 22, 26 would come into direct conduction.

In this manner, the conventional diodes are replaced by elements at avery low resistance, which drastically reduce the energy dissipated onthe rectifier bridge, thus increasing the yield of the voltage regulatordevice 10. With this type of drive, yields can be achieved that canexceed 95%, which allows, while keeping the energy supplied by theaccumulator 12 constant, using cooling systems that are drastically morereduced compared to the voltage regulators produced according to theconventional technique.

In order to be able to implement all the functions described above, thevoltage regulator device 10 according to the invention is provided withboth a microprocessor 28 generating the necessary drives for each MOSFET20, 24, and with specific interface drivers for driving the upper partand the lower part of the rectifier bridge. The algorithm used to drivethe MOSFETs 20, 24 when the wheeling diodes 22, 26 are proximate to thedirect conduction is indicated in FIG. 8. This algorithm provides for asynchronous drive of each MOSFET 20, 24, where the generator of therectifier bridge is implemented as follows:

if the voltage phase V_(fase) _(—) _(n) in the voltage regulator device10 is greater than or equal to the positive potential V_(batt) of thebattery 12, the first series of MOSFETs 20 is switched off, so as not toshort-circuit the battery 12, and the second series of power elements 24is switched on, so that the current can flow from the generator towardsthe battery 12 through a low resistance path, as the MOSFETs 24, and notthrough the wheeling diodes 26.

Similarly, if the voltage phase V_(fase) _(—) _(n) in the device 10 islower than or equal to the negative potential G_(batt) of the battery12, the second series of MOSFETs 24 is switched off, so as not toshort-circuit the battery 12, and the first series of MOSFETs 20 isswitched on, so that the current can flow from the generator towards thebattery 12 through a low resistance path, as the MOSFETs 20, and notthrough the wheeling diodes 22.

In this manner, it has been shown that the voltage regulator deviceaccording to the present invention implements the objects set forthabove.

The thus-devised voltage regulator device according to the presentinvention is anyhow susceptible of a number of modifications andvariations, all of which falling within the same inventive concept;furthermore, all the details can be replaced by technically equivalentelements. In practice, the used materials, as well as the shaped anddimensions, will be able to be any, according to the technical needs.

Therefore, the protection scope of the invention is defined by theannexed claims.

1. A voltage regulator device, applicable to the electrical system of amotor vehicle of the type comprising at least one electrical machineconsisting of a three-phase generator and at least an accumulator, thevoltage regulator device comprising a rectifier bridge and a voltagerising circuit provided with a first series of power elements,characterized in that the voltage rising circuit comprises one or moreinductors the winding inductance of stator phase of which is exploitedin order to raise the phase voltage above the level of the voltageprovided by the accumulator, so that it is possible to supply current tothe electrical loads of the vehicle since a very low rotation regime ofthe engine of said vehicle.
 2. The voltage regulator device according toclaim 1, characterized in that said first series of power elementsconsists of three N channel field-effect transistors of the MOSFET type,wherein it is possible to use the respective wheeling diodes asrectifier elements and the channel closure in order to perform theregulating and raising voltage functions.
 3. The voltage regulatordevice according to claim 1, characterized in that in the upper part ofthe rectifier bridge three diodes are present, the energy stored in theinductors further to the closing of a switch on the lower part of saidrectifier bridge being returned to the opening of said switch as extravoltage that permits to trigger said three diodes to supply currenttowards the accumulator.
 4. The voltage regulator device according toclaim 1, characterized in that in the upper part of the rectifier bridgea second series of power elements is present, consisting of three Nchannel field-effect transistors of the MOSFET type, wherein it ispossible to use the respective wheeling diodes as rectifier elementsduring the raising voltage phase.
 5. The voltage regulator deviceaccording claim 1, characterized in that it is equipped with amicroprocessor that generates the necessary driving for each series ofpower elements.
 6. The voltage regulator device according to claim 5,characterized in that it is equipped with interface drivers specific fordriving the upper part and the lower part of the rectifier bridge. 7.The voltage regulator device according to claim 5, characterized in thateach series of power elements is driven by the microprocessor through aseparate drive in the instant when the relative wheeling diode wouldcome into direct conduction.
 8. Driving method of a voltage regulatordevice according to claim 1, characterized in that it comprises thefollowing phases: if the voltage phase (V_(fase) _(—) _(n)) in thevoltage regulator device is greater than or equal to the positivepotential (V_(batt)) of the accumulator, a first series of powerelements is switched off, so as not to short-circuit said accumulator,and a second series of power elements is switched on, so that thecurrent can flow from the three-phase generator towards said accumulatorthrough a low resistance path as said second series of power elements,and not through the wheeling diodes; if the voltage phase (V_(fase) _(—)_(n)) in the voltage regulator device is lower than or equal to thenegative potential (G_(batt)) of the accumulator, said second series ofpower elements is switched off, so as not to short-circuit saidaccumulator, and said first series of power elements is switched on, sothat the current can flow from the three-phase generator towards saidaccumulator through a low resistance path as said first series of powerelements, and not through the wheeling diodes.